The present invention relates generally to telecommunications, and more specifically, to transmitting comfort noise across a mobile communications network, such as a third generation mobile system.
System Background
As terminal devices (also called mobile communication devices), such as mobile phones, Personal Digital Assistants (PDAs), and Mobile Computing Devices (PCDs), for example, continue to proliferate, mobile communications network providers are seeking to provide economical networks and radio protocols to deliver seamless service across multiple networks. Third generation mobile systems (3G systems), such as the Universal Mobile Telecommunications Systems (UMTS, now known as INT-2000), Mobile Broadband Systems (MBS), Wireless Local Area Networks (WLAN), and Global System for Mobile Communications (GSM) derivatives, for example, address the increasing demand for mobile communication services.
FIG. 1 (Prior Art) illustrates a generic 3G system of a GSM-type mobile communications network that incorporates both a mobile phone air interface and a satellite-phone air interface. Though the 3G system of FIG. 1 is illustrated as a GSM system, it should be understood that the 3G system architecture illustrated in FIG. 1 generally applies to any 3G system. In addition, though much of the following discussion is directed at unidirectional information flow (from a mobile phone to another terminal device), it should be understood that the flow of information may also take place in the opposite direction from that discussed.
Accordingly, a mobile phone 110, which could be any terminal device, is shown in communication with an antenna 114 across an air interface. Communications take place across the mobile phone air interface in a first channel 112 (and an optional second channel 116) which carries information, such as sound or data, between the mobile phone 110 and the antenna 114 as a data unit contained in a time slot 118. Then communications traveling through the antenna 114 pass to a Base Station (BS) 120 (which is also known as a Base Transceiver Subsystem, or BTS).
Similarly, a satellite-phone 170 uses a first channel 172a to transmit and receive information in a timeslot 178a, across the satellite-phone air interface, to or from a satellite 174. An optional second channel 176a is shown to illustrate that availability of multi-channel communications. The satellite 174 is one of a network of satellites that orbit the Earth, typically in a geosynchronous orbit. The satellite 174 provides for communication, perhaps by communicating with a second satellite (not shown), with the base station 122 via a first channel 172b and/or second channel 176b, and transfers information in a timeslot 178b. Although FIG. 1 illustrates communication occurring across the air interfaces in a single timeslot and in a single channel, it should be understood that communication in a 3G system may use multiple timeslots in a single channel, single timeslots in multiple channels, or multiple timeslots in a plurality of channels.
Traditionally, in a mobile communications network, the transfer of control commands (the pathway of which is called a control plane), and the transfer of user voice or data (the pathway of which is called a user plane), have occurred through the same transmission path and devices. However, one distinguishing characteristic of some implementations of third generation mobile communication systems is the physical separation of the control plane from the user plane. Accordingly, the connections which comprise the control plane are shown as dotted lines, such as a dotted line 180, which connects base station 120 with a control node 140 through a Radio Network Controller (RNC) 132. Likewise, the connections that comprise the user plane are shown as solid lines, such as a solid line 186, which connects the base station 120 with a media gateway 130 which in 3G will be a Transmission Control Node (TCN) 130.
Accordingly, the devices and connections existing on the land-based portion of the mobile communications network (called the Public Land Mobile Network, or PLMN) which transfer voice, data, or video information (collectively, xe2x80x9cinformationxe2x80x9d) between terminal devices define a user plane. Though the following discussion is directed at unidirectional information flow (from the mobile phone 110 to another terminal device), it should be understood that the flow of information also takes place in the opposite direction from that discussed. Thus, the user plane of FIG. 1 is defined by the route information travels from the antenna 114, through the BS 120, and on to the media gateway 130. The user plane continues from the media gateway 130 to a core transport network 150 that passes information onto a media gateway associated with the other terminal device. For example, if the other terminal device were the satellite-phone 170, the media gateway base station controller combination MGW/BSC 138, and the second base station 122 would further define the user plane. A control plane is similarly defined by the devices that execute the control commands in a PLMN, and the pathway the control commands travel from device to device in the PLMN.
To control the transfer of information through the third generation mobile system, the control node (CN) 140 [which is associated with a Mobile Switching Center (MSC) in a second generation system, or, as shown here, is a UMSC (UMTS Mobile Switching Center) server in 3G GSM] communicates with the base stations 120, 122, as well as the media gateways 130, 132, 134, 136 and MGW/BSC 138. Thus, the UMTS server 140 directs control commands traditionally associated with a control channel signal in second generation and first generation mobile communications systems. By separating the control plane and the user plane, user data can be transferred more efficiently between media gateways, and the control plane can be separately configured for Quality of Service and security. Thus, 3G systems employing this architecture increase flexibility and transmission efficiency in the transport network.
Though the third generation mobile system of FIG. 1 is illustrated as a 3G Global System for Mobile Communication (GSM), it should be understood that the 3G system architecture illustrated in FIG. 1 generally applies to any third generation mobile system. Thus, while the media gateway 130 will be a Base Station Control (BSC) in second generation GSM, it will be a Radio Network Controller (RNC) or Transmission Control Node (TCN) in UMTS.
Channel Communications and Transport Network Communications
In GSM, sound communications (or hereinafter, xe2x80x9cvoice communicationsxe2x80x9d) pass across an air interface in at least one channel, in a discreet time unit known as a frame. Each frame is subdivided into a number of smaller discrete time units, known as timeslots. For example, in GSM, a single frame is subdivided into eight timeslots. Each timeslot is further divided in time into bit slots, and the bit slots are organized so that the time slot can accommodate two words of 57 bits each, as well as other bits that are needed for the transmission of the words. Similar methods of time division as well as frequency division are used across the air interfaces associated with other mobile communications networks.
In operation, to provide for predictable communication, each mobile phone call is assigned at least one time slot in a frame. However, to improve communication quality or throughput, multiple timeslots (in a single frame) in a single channel, a single timeslot in multiple channels, or multiple timeslots in a plurality of channels may be allocated to a communication.
A collection of bits representing voice communication, whether organized as a word or other assemblage, is referred to as a voice data unit. Typically, when transferring voice communications, voice samples (or data units) arriving from a mobile phone are interleaved and extracted in the base station 120 until a predetermined number have accumulated. Once the predetermined number of voice data units have extracted, the BS passes the data units to the originating TCN 130, which assembles the voice data units into whatever format is needed by the core network 150. Typical core networks include Internet Protocol (IP) networks, and Asynchronous Transfer Mode (ATM) networks, for example.
Accordingly, a voice data unit is (or voice data units are) transferred across a mobile communications network in ATM cells or IP packets (the ATM cell or IP packet contains the voice data units, which are referred to as the xe2x80x9cpayloadxe2x80x9d of the IP packet or the ATM cell). More specifically, the core transport network 150 accepts the data units from the TCN 130 and provides routing to a destination media gateway (MGW), such as the second MGW 132, which is in communication with a public switched network (PSTN) 162. Of course, the voice data units could pass to other destination media gateways, which could be TCNs, such as a third MGW 134, which is in communication with an ATM network 164, a fourth MGW 136 which is in communication with an IP based network 166, or the fifth MGW/BSC 138, which is in communication with the second base station 122.
Parties to a communication, such as a conversation, produce sound (i.e., talk) about 40% to 60% of the time they are actually occupying the communication channel. In other words, the audible sounds produced by the parties to a conversation are typically about 40% to 60% silence. However, if xe2x80x9ctrue silence,xe2x80x9d meaning no noise at all, is transmitted across the network, the parties often misinterpret the absence of noise as an indication of a problem with the communication. Thus, to provide the parties to the conversation assurance that the communication is working, some level of xe2x80x9ccomfort noisexe2x80x9d (or silent noise) is sent across the network when the parties are not speaking.
Accordingly, to provide for comfort noise, the BS receives the xe2x80x9csilencexe2x80x9d information from a terminal device and uses these samples of silence to take the place of what would otherwise be speech samples. These samples are converted into voice data items, and are then placed in the payload portion of IP packets or ATM cells and are sent across the mobile communications network. Unfortunately, because it can take as much payload to transfer silence as it does to transfer actual voice communication, there is a high price to pay for the transport of this xe2x80x9csilencexe2x80x9dxe2x80x94 a tremendous amount of processing (approximately 40%, and as much as 60%, of a mobile communications network processing effort) is spent transferring silence (or comfort noise).
Therefore, there exists the need for a system, method and computer program for transmitting, across a mobile communication network, comfort noise and that reduces the processing requirements of the prior art.
The present invention achieves technical advantages as a system, computer program, and method for transmitting, across a mobile communication network, the occurrence of silence in a communication channel. When silence is detected on an upstream communication channel at a BS, either directly or as a silence identifier (SID), a network SID is generated to indicate silence on the communications channel. The network SID is received by a destination TCN, which then generates comfort noise in a destination terminal device. By using the network SID, the present invention reduces the processing demands needed to provide for silent noise detection and comfort noise generation.
In one embodiment, the present invention is a system for transmitting, across a mobile communication network, the occurrence of silence in a communication channel. The system generally comprises a control node, a first transmission control node (first TCN) for executing a silence transmission algorithm, and a second transmission control node (second TCN) for executing a comfort noise generating algorithm. The first TCN and the second TCN are in communication with the control node in a control plane. A core transport network couples the first TCN to the second TCN in a user plane.
In another embodiment, the present invention is a method for transmitting, across a mobile communication network, the occurrence of silence in a communication channel. The method comprises the steps of detecting silence in a communications channel, and transmitting a network SID. Then, either as a continuation of the present method, or as an independent method, a network silence indicator (SID) is received, and comfort noise is produced.
In yet another embodiment, the present invention is a computer program. The computer program comprises a query module for detecting a comfort noise production module in a destination TCN, and a network SID transfer module for placing a network SID on the mobile communications network.